The present study first investigated the photocapacitance measurements of Al/p-Si/ZnO:Coumarin/Au metal-oxide-semiconductor MOS device at room temperature in the frequency range of 10 kHz-1MHz and bias voltage range of −5 V; +5 V. Based on photocapacitance analysis, Vbi, Na, Nss, Ef, Em, Δϕb, ϕb, Wd values were calculated for 10 kHz, 100 kHz and 1 MHz. For 1 MHz, Vbi value was 0.79 eV, Na value was 3.54x1015 cm−3, ϕb value was 0.99 eV and Wd value was 530 nm. Additionally, the dielectric constant (ε′), dielectric loss (ε″), electrical modulus (M′M″) and complex impedance (Z*), tangent loss (tanδ), ac conductivity(σac) and phase angle (φ) values of the device were also calculated. ε′ values were calculated 116 at 10 kHz, 58 at 100 kHz and 6 at 1 MHz. These ε′values indicate that the higher ZnO:Coumarin layer can store more charge carriers. This study has shown that materials produced by ZnO, a metal oxide semiconductor, doped with coumarin have the potential to be used in many optoelectronic devices, especially in photonic applications.